KB backrest : Development of an adjustable backrest for wheelchairs (English)

Abstract [en]

This master thesis is commissioned by Permobil AB. The report describes thoroughly the developing process of an adjustable backrest for wheelchairs. The target group for the backrest are people that suffer from scoliosis or other spinal diseases. Because of insufficient pressure distribution usage of traditional backrests is not an option for them.

The current solution has got a frame that is made by several adjustable links that is held in place by friction. Between the links velcro tapes are attached that is adjusts the depth. The links are fixated by screw joints that need to be tightened real hard to keep the links shape correct during usage, which is not user friendly. The KB backrest is a part of the KB seat that is disappearing from the company’s assortment. Permobil want to keep the backrest as an optional component for the more versatile Corpus seat because of its unique abilities. The Corpus seat is also in development and before the KB backrest can be included its negative sides needs to be corrected, which this project aims to do.

Primarily the work has focused on the locking mechanism that is needed to fixate the parts of the backrest. The greatest challenge during the project was to achieve an easily manoeuvred lock that fixates the system properly and at the same time admit a great range of adjustment with few parts.

The final concept has seven links on each side of the frame with the same sort of velcro tapes between them. Using more links gives a frame that follows the users back profile more exact and smaller gaps between the tapes. This leads to better abilities concerning even pressure on the users back. A clamping lever with eccentric cam is used to push together cog shapes on the links ends for total locking. The upper link that connects the frame sides has been given an angle backwards to further ease the upper tapes function in depth.

The concept needs more thorough testing, mainly concerning component strength, for further enhancements and final realisation. The qualities the concept brings concerning easy adjustment and locking is recommended to be taken under consideration for further development.